1. Field of the Invention
The invention relates to a grinding wheel.
2. Description of the Related Art
Grinding stones are conventionally used to grind journals, crank pins, and the like for an automotive crank shaft. See, for example, Japanese Patent Application Publication No. H11-188640 (JP H11-188640 A). A grinding stone disclosed in JP H11-188640 A has a disc-like member forming a grinding wheel and a grinding stone. The grinding stone is provided on an outer peripheral surface of the disc-like member, includes two types of grinding stone layers with different properties, and is divided into chips. Specifically, during grinding, high grinding resistance is offered at opposite end corners of the outer peripheral surface of the disc-like member in the direction of an axis of rotation and on opposite end surfaces of the outer peripheral surface. Thus, in these areas, a grinding stone layer is provided which is formed of grinding grains with a large grain size and which is unlikely to be worn away. No high grinding resistance is generated in a cylindrical portion between the opposite end corners of the outer peripheral surface. Thus, in this area, a grinding stone layer is provided which is formed of grinding grains that have a small grain size and are likely to worn away and that are expected to achieve high finishing accuracy.
In the above-described grinding stone, the two grinding stone layers are laminated to each other so as to have a joint surface in a direction orthogonal to the axis of rotation of the grinding wheel; one of the grinding stone layers is located at the end corners and on the end surfaces that involve high grinding resistance and that are likely to be significantly worn away, and the other grinding stone layer is located on the cylindrical portion that involves low grinding resistance and that is unlikely to be worn away. The grinding stone layers as described above are located adjacently to each other in the direction of the axis of rotation and simultaneously used for a grinding operation. Consequently, the grinding stone layers are worn away to different degrees, and thus a large step is likely to be formed at the joint surface, which is a boundary portion.